The organization of the efferents of the olfactory bulb (OB) of the rat will be mapped by stimulation of terminals of the lateral olfactory tract (LOT) as they enter the olfactory projection areas. Antidromic activation of single mitral or tufted cells will be observed and the size of the OB field potential will be mapped. The physiological properties of regions of the OB will be correlated with the position and extent of their projections. Odor responses of single units with known projections will be studied by construction of post stimulus histograms and analysis of their statistical properties. Local OB responses will also be studied by obseving the magnitude of the averaged induced wave which is synchronized by LOT stimulation. There are two purposes of this study. First, anatomical data show that the olfactory tubercle receives afferents from a special part of the OB and physiological data show that hypothalamic odor responsive neurons which receive olfactory afferents from the tubercle have response properties which differ from other parts of the olfactory system. This study will investigate to what degree this is a result of the organization of the OB output. Second, the organization of the projection of the OB is not well understood. Althouggh anatomical data show that there is no single, well defined point-to-point representation of the OB on the olfactory cortex, other organizational patterns are possible and can be tested by the procedure proposed. Studies will be made of degree of habituation of odor responses of neurons of olfactory tubercle and cortex. The study will show what sorting of olfactory information takes place before the activa$ion of cells of the olfactory projection areas and provide a basis for the study of processing in these areas.